TLB Partitioning with Victim Buffer for Hot Set Management
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Solution Overview
Problem
The hot set problem in translation lookaside buffers (TLBs) leads to increased TLB misses, degrading performance due to uneven distribution of virtual addresses by hash functions, resulting in overused and underused sets.
Innovation Solution
Implementing a victim TLB that reduces the number of ways allocated to each DTLB set, repurposing those to store evicted translations, and using a victim TLB hint bit to identify hot sets for targeted storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of ways in each TLB set is increased to reduce hot set problem, then TLB miss rate decreases, but circuit area increases
Solution Approach 1:
The patent segments the TLB structure by separating ways into two categories: primary ways for normal translations and victim ways specifically for evicted translations from hot sets. This segmentation allows the TLB to maintain high hit rates for frequently accessed translations without requiring a uniform increase in all ways, thus reducing the overall circuit area compared to a fully increased TLB structure.
Solution Approach 2:
The patent applies local quality by making different ways serve different functions within the same TLB set. Victim ways are specifically optimized to hold evicted translations from hot sets, while primary ways handle normal translations. This localized specialization allows the system to improve performance in critical areas (hot sets) without proportionally increasing the entire TLB area.
2Reliability
If a victim TLB is implemented to store evicted translations, then TLB misses are reduced, but device complexity increases
Solution Approach 1:
The patent implements dynamic functionality by enabling ways to transition between primary and victim roles based on translation eviction events. The same physical structure can adapt its function dynamically - ways become victim ways when they need to hold evicted translations and return to primary function when evictions cease. This dynamic adaptability reduces the need for permanent structural additions that would increase complexity.
Solution Approach 2:
The patent makes TLB ways universal by allowing them to serve multiple functions: primary ways can become victim ways and vice versa. This multi-functionality is achieved through the eviction detection mechanism that identifies when translations are evicted from hot sets and should be retained in victim ways. The same hardware structure performs different roles based on runtime conditions, reducing overall device complexity.
3Productivity
If the TLB structure is modified to accommodate victim buffering, then performance is maintained, but manufacturing complexity increases
Solution Approach 1:
The patent changes operational parameters rather than physical structure to achieve victim buffering. By modifying the eviction detection logic and using existing ways with different functional states, the system achieves performance benefits without adding physical components that would complicate manufacturing. The solution relies on parameter changes in how existing hardware is utilized rather than hardware modifications.
Data Source
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AI summary
Techniques for victim buffering through translation lookaside buffer (TLB) partitioning are described. In certain examples, a system includes a memory; an execution circuitry to generate a memory access request for a virtual memory address of the memory; a first level translation lookaside buffer to store virtual address to physical address mappings; a victim translation lookaside buffer to store a virtual address to physical address mapping evicted from the first level translation lookaside buffer; a second level translation lookaside buffer; and a cache coherency circuitry to search the first level translation lookaside buffer and the victim translation lookaside buffer for a corresponding physical address mapped to the virtual memory address for the memory access request, and for a miss in the first level translation lookaside buffer and the victim translation lookaside buffer, search the second level translation lookaside buffer for the corresponding physical address mapped to the virtual memory address for the memory access request, and for a hit in the victim translation lookaside buffer, provide the corresponding physical address mapped to the virtual memory address for the memory access request.